The active compound in marijuana, THC, can slow the growth of lung tumours and reduce the spread of the cancer in mice, a preliminary study reveals. They hope that drugs mimicking the apparent anti-cancer effects of tetrahydrocanabinol (THC) could one day help treat patients. Ramesh Ganju at the Harvard Cancer Center in Boston, Massachusetts, US, and colleagues deposited human lung cancer cells under the skin of a dozen mice and allowed the tumours to grow in the animals for about two weeks. They then began giving half of these mice daily injections of about 250 micrograms of synthetic THC right...